Certain pressure measuring devices, in particular also such as those that include micromechanical pressure sensor elements, are conventional. They are presently firmly established in automotive engineering and are used in that area for multiple functions. Typical applications are, for example, detection of intake manifold pressures and charge pressures for optimizing the engine control.
In addition to sensors in analog circuit technology, which have been available for many years, lately micromechanical pressure measuring devices, implemented in digital circuit technology, are being increasingly marketed. The underlying objects of signal processing have remained essentially the same. One main object of the downstream electronic analyzer circuit is the elimination of the temperature dependency of the micromechanical sensor element. In particular when piezoresistive pressure sensor elements are used, this elimination is very important for being able to achieve high measuring accuracy over the entire temperature range because of the strong temperature dependency of the piezoresistive transduction constant.
In analog pressure measuring devices the temperature dependency is compensated for by using a temperature-dependent supply voltage, which is reciprocal to the temperature dependency of the piezoresistive transduction constant.
In digital pressure measuring devices a piezoresistive bridge is supplied with a constant voltage, the output voltage is digitized with the aid of an analog-digital converter, and the temperature dependency of the signal is subsequently corrected with high precision via digital signal processing.
Both of the above-described methods have disadvantages due to their principle of operation.
Emulating the reciprocal temperature-dependent bridge supply voltage is only achievable with limited accuracy in analog circuit technology, since in this case components having non-linear characteristics are needed, which cannot be easily adjusted in a targeted manner. In addition, the adjusted curve may change over time due to drifts, so that impaired accuracy over the service life of the pressure measuring device is to be expected.
Although the digital correction method does not have these disadvantages, the correction in digital signal processing may be set with high accuracy and therefore made constant over the service life of the component. However, in this method, a high output voltage range of the pressure sensor element over the temperature is accepted, which must be taken into account in the input voltage range of the analog-digital converter. As a result, the achievable accuracy of the analog-digital conversion decreases.